This project aims to characterize the receptors for Phe-Met-Arg-Phe-NH2 (FMRFamide) and Phe-Leu-Phe-Gln-Arg-NH2 (NPFF) in mollusk and mammalian CNS, respectively. Radioactive analogs of NPFF and FMRFamide were prepared for developing receptor binding assays in membrane preparations. A multichannel perfusion apparatus was constructed to study the effects of NPFF on secretion of oxytocin and vasopressin from isolated nerve endings of the rat neural lobe. An antibody to a cAMP analog was characterized in a cAMP RIA to measure neuropeptide-stimulated adenylate cyclase activity in membrane preparations. The proposed course of this project includes (1) study of ligand binding to NPFF receptors, (2) development of specific NPFF antagonists, (3) investigation of the coupling of NPFF receptors to cellular signal transduction systems, (4) study of the physiological and behavioral effects of NPFF and its antagonists, including interactions with opiods, and (5) isolation of NPFF and FMRFamide receptors from bovine and squid CNS respectively.